This disclosure relates generally to air bags for vehicles. More particularly, this disclosure relates to air bag covers and methods of forming air bag covers having a weakened region defined in a polymeric foam, where the weakened region allows the cover to open during air bag inflation.
Air bag modules have become common in modern automobiles. An air bag module comprises an inflatable cushion and an inflator. The module is installed in a desired position within the vehicle. The cushion is stored in a folded position within the air bag module. In response to a threshold event or occurrence, a sensor provides a signal for activating the inflator. The inflator provides a supply of inflating gas to the cushion to inflate the cushion.
The air bag module is provided in a desired location, such as the steering wheel, the dashboard, the seat, the A-pillar, and other locations. A cover is often placed over the air bag module to conceal and protect the contents of the module. The inflation of the cushion applies a force on the cover to tear or open the cover along one or more weakened regions formed in the cover. Thus, the weakened regions allow the cover to open during air bag inflation.
In order to provide an aesthetically pleasing appearance, it is desired to hide the weakened regions from the user. It is also desired that the weakened regions open in a controlled and repeatable manner regardless of the temperature condition and/or deployment level of the air bag module.
It is also desired to provide the weakened region with a thickness that eliminates the difficulties that may arise during the manufacture of the cover. Further, it is also desired to provide the weakened region with a thickness that eliminates the undesired appearance factors that may arise in covers. For example, during conventional injection molding of prior covers the weakened region has been formed as a thinned section of the cover. This thinned section can cause a restriction in the flow of the polymer material through the mold at the weakened region. This flow restriction creates a zone of high shear stress in the weakened region. The high shear stress zone may affect, for example, the finished surface of the region. Namely, the elastic nature of the polymer may cause the stress in the region to rebound once the cover has been released from the molding tool, which can cause a bump on the surface of the cover. Additionally, the combination of the thin/thick sections caused by the weakened region also creates non-uniform shrinkage/expansion of the cover along the weakened region during the temperature cycling to which the vehicle is exposed. The non-uniform shrinkage along this weakened region may show up as a bump or ridge on the surface facing the vehicle or show surface, thus providing a potentially displeasing aesthetic appearance.
One prior solution to the problems of restricted polymer flow through the mold and the non-uniform shrinkage/expansion of the cover along the weakened region is to increase the thickness of the thinned portion. However, increasing the thickness requires additional materials and cost.
Accordingly, continuing developments in the design and manufacture of air bag covers are desired to provide covers that meet the desired aesthetic properties and functional requirements.
A cover for an air bag module is provided. The cover comprises a polymeric sheet and one or more thinned portions. The polymeric sheet has a first surface and a second surface and includes a plurality of cells formed therein. A skin is formed on at least the first surface. The thinned portions are formed in the second surface and define a weakened region of the cover.
A cover for an air bag module comprising a foamed polymeric sheet and a weakened region is provided. The foamed polymeric sheet has a show surface, a non-show surface, and a skin formed on at least the show surface. The weakened region is formed by one or more thinned portions defined in the non-show surface.
An air bag module is provided having a housing, an inflatable cushion, an inflator, and a cover comprising a foamed polymeric member. The housing is positionable in a cavity of a vehicle. The inflatable cushion and inflator are stored in the housing such that the inflator is in fluid communication with the inflatable cushion. The foamed polymeric member has a show surface, a non-show surface, and a weakened region. The weakened region is defined by one or more thinned portions. The non-show surface covers the housing proximate the inflatable cushion whereby inflation of the inflatable cushion by the inflator causes the inflatable cushion to expand into the cover, and thus to apply a force on the cover to tear or open the cover along the weakened region thereby providing an outlet for the inflatable cushion through the cover into the vehicle.
A method of making a cover for an air bag module is provided. The method comprises mixing a blowing agent and a molten polymer under a first condition, the first condition being sufficient to prevent the blowing agent from forming bubbles in the polymer; changing the first condition to a second condition, the second condition being sufficient to cause the blowing agent to form bubbles in the molten polymer; and molding the molten polymer containing the bubbles into a desired shape in a mold, the desired shape comprising a first polymer sheet having a plurality of first cells being defined therein and a thinned portion being defined in a first surface of the first polymer sheet.
A method of controlling the density of a region of a foamed polymer is also provided. The method comprises mixing a blowing agent and a molten polymer under a first condition, the first condition being sufficient to prevent the blowing agent from forming bubbles in the polymer; changing the first condition to a second condition, the second condition being sufficient to cause the blowing agent to form bubbles in the molten polymer; molding the molten polymer containing the bubbles into a desired shape in a mold, the desired shape including a plurality of first cells being defined within the desired shape by the bubbles; and moving a portion of the mold disposed at the region from a first position to a second position, movement of the portion of the mold causing the first cells in the region to change to second cells without changing the first cells in remaining regions of the foamed polymer, the foamed polymer having a first density at the remaining regions caused by the first cells and a second density at the region caused by the second cells.
The above-described and other features are appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims.